I would be very careful with the book of Mr. Friebe and especially what he said about the Varus battle. There is very convincing evidence that the dip near Kalkriese was the place of the battle. Of course some things are still problematic (f.e.discussion about the coins found, a sword sheath part with a inscription of the legio I and so on) but these are minor concerns.

The distinction between Celts and Germanics is difficult and has an artificial element. The Celts had an urban culture (oppidae) which the Germanics normally had not, but even there were seemingly mixtures. The Germanics were at least heavily influenced by the Celtic culture.